Measurement system for small divergence of laser beam

The accurate measurement of beam divergence, particularly small divergence, is important and necessary to assess the collimation of a laser beam for space communication and distance measurement applications. To solve the practical problem that the small divergence of a laser beam is difficult to be effectively measured using the existing divergence measurement methods, a two-lens detection technique for small divergence is proposed based on the lens focal-plane detection method, the measurement principle of the technique is analyzed on the basis of property of propagation of laser beam through a lens, and a measurement system with a large-aperture(phi =300mm), long-focal-length(f =3500mm) lens is developed, which can realize the accurate measurement of small divergence (8-500murad). The system can also act as an autocollimator for fine measurement of small angles with the accuracy of 0.3".